The trendy, high-tech learning tool, used to take attendance, poll student opinion, and administer quizzes, is taking hold on campuses across the country, with an estimated two million college students now using them, transforming teaching - and learning.

"I think they are the greatest educational innovation since chalk," said Neil Sheflin, an associate professor of economics at Rutgers University.

The use of clickers, which can cost $35 to $45 apiece, is shifting education away from the age-old practice of putting a professor at the front of a room to lecture to a passive audience. Instead, it forces participation from all students and encourages peer learning. It is, as one pair of professors titled a journal article, like "waking the dead."